FI128623B

FI128623B - Process and apparatus for treating manure sludge

Info

Publication number: FI128623B
Application number: FI20165667A
Authority: FI
Inventors: Antti-Pekka Partonen; Antti Heino; Harri Kallioinen
Original assignee: Valio Oy
Priority date: 2016-09-07
Filing date: 2016-09-07
Publication date: 2020-09-15
Also published as: RU2720866C1; WO2018046799A1; CN109689596A; EP3510006B1; ES2968423T3; FI20165667A; EP3510006C0; EP3510006A1

Abstract

The invention relates to a method for treating manure sludge comprising the steps of: providing manure sludge; subjecting the manure sludge to separation to provide a first dry fraction and a first liquid fraction; subjecting the first liquid fraction to centrifugation to provide a second dry fraction and a second liquid fraction; subjecting the second liquid fraction to one or more sequential reverse osmosis (RO) filtration steps to provide one or more RO retentates and one or more RO permeates, wherein the feed for each subsequent RO filtration step is an RO permeate obtained from the previous RO filtration step.

Description

PROCESS AND APPARATUS FOR TREATING MANURE SLUDGE

FIELD OF THE INVENTION The present invention relates to agricultural and separation technolo- gies. More particularly, the invention relates to treatment of manure sludge by means of separation technologies.

BACKGROUND OF THE INVENTION Today's milk production and animal rearing are highly centralized. Thus, animal farms increase in size and large amounts of manure sludge are gen- erated locally. A large manure sludge amount results in logistic problems as the manure must be spread over a large field area within a short period of time. Ma- nure must then be transported over long distances, which incurs costs. Further, significant investments are required in spreading equipment. As animal farms increase in size, rationalizing the treatment of manure sludge is more important than ever. The size of present manure sludge containers is about 1 000 to 8 000 m3, which means that there is a great need for dewatering, or concentration, ma- nure sludge.

Spreading of manure sludge onto fields is nowadays restricted by the high phosphorous content of the manure. Hence, even for ecological reasons, there is a need for developing the treatment of manure sludge further to allow manure sludge and its valuable components to be utilized in a more efficient manner than before.

FI patent application 20126072 discloses a process for treating ma- nure sludge wherein homogenous manure sludge is subjected to microfiltration, and the obtained microfiltration permeate is concentrated in one or more reverse N 25 osmosis step. N Nutrient recirculation, prevention of eutrophication of water system 3 and so-called bioeconomy are topic issues worldwide. ™~ We have now found an enhanced process for treating manure sludge = wherein the manure is efficiently dewatered and the nutrients are efficiently sep- N 30 arated into different fractions.

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O BRIEF DESCRIPTION OF THE INVENTION > An object of the present invention is to provide a method for treating manure sludge comprising the steps of: - providing manure sludge,

- subjecting the manure sludge to separation to provide a first dry fraction and a first liquid fraction, - subjecting the first liquid fraction to centrifugation to provide a second dry frac- tion and a second liquid fraction, - subjecting the second liquid fraction to one or more sequential reverse osmosis (RO) filtration steps to provide one or more RO retentates and one or more RO permeates, wherein the feed for each subsequent RO filtration step is an RO per- meate obtained from the previous RO filtration step and wherein the dry matter content of the permeate obtained after one or more RO filtration steps is <0.5%.

The present invention provides an efficient method for separating wa- ter and solid matter of manure sludge. An advantage of concentration of manure sludge is that transportation of water is reduced. This again reduces transporta- tion and spreading costs, decreases the compaction of arable land and makes it possible to utilize the manure nutrients more efficiently.

The invention further provides a method in which nutrients, such as phosphorus, nitrogen and potassium present in manure sludge, are efficiently separated into different fractions. In the method, phosphorus is mainly retained in the dry fractions obtained in the method while nitrogen and potassium are fair- ly uniformly divided between the dry and liquid fractions. This enables optimal use of the various fractions obtained in the method in an appropriate manner.

The invention further provides a method which produces a high amount of a water fraction with ultimately low chemical oxygen demand (COD) and low nitrogen, potassium and phosphorus contents.

The invention still further provides a method which produces a liquid fraction which contains a high amount of nitrogen but is substantially free of o phosphorus. AN An advantage of the invention is also that the spreading of manure A sludge is enhanced, since nutrient-containing fractions can be more efficiently 7 spread compared with untreated manure sludge. Further, there are economic and A 30 environmental advantages, including savings in spreading costs, more accurate E dosing of certain nutrient in fertilization, better nutrient response, no need of ad- N junct spreading area reguired by the regulatory issues, and less manure storage. O Another object of the invention is to provide an apparatus for treating = manure sludge comprising: N 35 —-aseparator unit for separating manure sludge to a dry fraction and a first liquid fraction,

- a centrifuge configured to receive the first liquid fraction from the separator unit and to remove solid matter from the first liquid fraction to provide a second lig- uid fraction, - one or more reverse osmosis (RO) units, one of which is configured to receive the second liquid fraction from the centrifuge and to concentrate the second lig- uid fraction, wherein the feed for each subsequent RO units is an RO permeate obtained from the previous RO unit.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an embodiment of the method of the invention; Figure 2 shows an embodiment of the method of the invention and il- lustrates the circulation of various fractions obtained in the method; Figure 3 shows an embodiment of the apparatus of the invention.

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a method for treating manure sludge comprising the steps of: - providing manure sludge, - subjecting the manure sludge to separation to provide a first dry fraction and a first liquid fraction, - subjecting the first liquid fraction to centrifugation to provide a second dry frac- tion and a second liquid fraction, - subjecting the second liquid fraction to one or more sequential reverse osmosis (RO) filtration steps to provide one or more RO retentates and one or more RO permeates, wherein the feed for each subsequent RO filtration step is an RO per- meate obtained from the previous RO filtration step. S 25 The manure sludge used in the method of the invention can be derived N from any animal. Typically, manure sludge is derived from cattle or pigs. 3 In the method of the invention, the manure sludge is typically treated ™~ at its natural temperature. If appropriate, the method can comprise a heating step = or a cooling step at any stage during the method in order to enhance the separa- + 30 tion of the nutrients. S Figure 1 illustrates an embodiment of the method of the invention. In © this embodiment, two reverse osmosis filtration steps are involved. The dashed N lines indicate optional embodiments of the invention. The fractions typed in italic letters represent final products which can be used as a ready-to-use nutrient- containing preparations as fertilizers, for example.

The dry matter content of manure sludge to be treated is typically in the range of about 1 wt% to about 15wt%. The chemical oxygen demand of ma- nure sludge is typically >15000 mg O2/L. Nitrogen, phosphorus and potassium in the manure sludge are typically present in a ratio of N:P:K of 3-10:1:3-10.

In the method, the manure sludge is subjected to a separation step to remove the coarsest solids from the sludge. Any device which provides separation of solid matter from liquid can be used. For example, separation can be carried out by filtering, centrifugation, sieving optionally using pressure, or with mechan- ical separators, including drum filter, screw press or disc filter. Separation can also be carried out by pressing the manure through gauze. In an embodiment, the separation is carried out with a screw press. Separation provides about 15 wt% to about 35 wt% of a dry fraction and about 65 wt% to about 85 wt% of a liquid fraction. The dry matter content of the dry fraction is about 15 wt% to about 35 wt%. The dry matter content of the liquid fraction is about 1.5 wt% to about 5 wt%. N:P:K ratio of the dry fraction is in the range of 2-4:1:1-2. The dry fraction obtained from the separation is a ready-to-use nutrient-containing fraction which can be spread onto the soil.

The separation step can be enhanced by washing whereby the transfer of soluble dry matter minerals and/or nutrients to the liquid fraction is increased.

Washing can be carried out by using one or more liquid fractions which are ob- tained in subsequent steps of the method of the invention.

In addition to washing or alternatively, additives can be added in the separation step to enhance the separation of solid matter, minerals and/or nutri- ents.

Prior to the separation step, manure sludge can be mixed to provide S mixed manure sludge. Mixing of the manure sludge provides more stable operat- N ing conditions during the process. Any mixing device is suitable which produces a A fairly homogenous mass of manure sludge, which is further led to the separation P step. = 30 The liquid fraction derived from the separation is led to centrifugation E to dewater the liguid fraction. Centrifugation means herein a process using a de- N vice, that is to say a centrifuge, which employs a high rotational speed to separate O components of different densities. In an embodiment, the drum speed of the cen- = trifuge is in the range of 2000 to 5000 rpm. In another embodiment, the differen- N 35 tial speed of the centrifuge is in the range of 0 to 20 rpm. In an embodiment, the centrifugation is carried out with a decanter centrifuge. Dewatering chemical(s)

can be added to the liquid fraction before centrifugation to increase the dewater- ing capacity of the centrifuge and to enhance the separation of at least one of solid matter, minerals and nutrients, such as phosphorus from the liquid fraction. Suit- able dewatering chemicals include, but are not limited to, metal salt coagulants, 5 such as ferric sulphate, and cationic, anionic or nonionic flocculation polymers. The above dewatering chemicals can also be used in various combinations. In an embodiment, metal salts coagulants are added in an amount of 0.01 to 5.0 kg/kg total solids of the manure sludge. In another embodiment, the cationic, anionic or nonionic flocculation polymers are added in an amount of 0.01 to 5.0 kg/kg total — solids of the manure sludge, optionally including the metal salts coagulants. Dy- namic or static mixers can be used to enhance the mixing of the liquid fraction and the chemical(s). Centrifugation of the liquid fraction derived from the separation pro- vides about 10 wt% to about 20 wt% of a dry fraction and about 80 wt% to about 90 wt% of a liquid fraction based on the feed subjected to centrifugation. The amount of the dry fraction from centrifugation corresponds to about 5 wt% to about 15 wt% based on the total amount of starting manure sludge. The dry matter content of the dry fraction and that of the liquid frac- tion obtained from the centrifugation are about 15% to about 25%, and about

0.1% to about 2.0%, respectively. N:P:K ratio of the dry fraction is in the range of 1-3:1-2:1. The dry fraction obtained from the centrifugation is a ready-to-use nu- trient-containing fraction which can be spread onto the soil. This dry fraction can be mixed with the dry fraction obtained from the previous separation step. The liquid fraction obtained from the centrifugation is further subject- ed to one or more sequential reverse osmosis (RO) filtrations to still remove dry S matter from the liguid fraction and to lower the COD value thereof. When a plu- N rality of RO filtration steps are carried out, in each filtration step the feed is the A permeate fraction obtained from the previous RO filtration step. ? Before the liguid fraction from the centrifugation is subjected to one or == 30 more RO filtrations, this fraction can be led through a sieve with a mesh size of E 10-500 um to remove solid matter from the liquid fraction. N In the reverse osmosis plant, the liguid from the centrifugation step, O optionally sieved, is concentrated while water is removed. Reverse osmosis pro- = vides a retentate, that is a concentrate, which is a fraction retained above the N 35 membrane, and a permeate which is a fraction passed through the membrane. The reverse osmosis filtration concentrates the nutrients which are mainly nitro-

gen and potassium to the retentate fraction. It is thus highly desirable to finally obtain a permeate fraction which is substantially free of dry matter and nutrients and is mainly pure water. The removal of nutrients of the liquid fraction obtained from the centrifugation and the production of pure water as an RO permeate are enhanced using more than one RO filtration step.

In the first RO filtration step, a volume concentration factor (VCF) of 5 to 15 is used. In the subsequent RO filtration steps, VCF of 10 to 80 is used. In an embodiment, the VCF is 50 in said further RO filtration steps.

RO filtration provides a liquid retentate that can be used, e.g. as a lig- uid fertilizer.

In an embodiment, the liquid fraction obtained from the centrifugation is subjected as a feed to two successive RO filtration steps wherein the permeate obtained from the first RO filtration is subjected to a second RO filtration. The retentate from the second and subsequent RO filtration steps are either fed to the — first RO filtration step together with the liquid fraction feed, or mixed with the retentate obtained in the first RO filtration step. The dry matter content of the retentate obtained after the first RO filtration steps, optionally including one or more retentates derived from the subsequent RO filtration steps, is about 1 wt% to about 15 wt%. N:P:K ratio of the retentate obtained after the first RO filtration — step, optionally including one or more retentates derived from the subsequent RO filtration steps, is in the range of 1:0:1-2.

The dry matter content of the permeate after one or more RO filtration steps is <0.5 wt%. The permeate is mainly water. The COD of this permeate is <15 mg O2/L. N:P:K ratio of the permeate derived from one or more RO filtration steps is 1-2:0:1. The initial feed for the RO step, that is the liquid fraction from the cen- S trifugation, is divided in the one or more RO filtration steps so that about 10 wt% N of retentate and about 90 wt% of permeate are formed. A The circulation of the various fractions obtained in the method of the 7 invention is illustrated in Figure 2. The dashed lines indicate optional embodi- A 30 ments of the invention. For example, the dry fractions from the separation and E centrifugation can be mixed and spread like dry manure onto the soil as a dry fer- 5 tilizer, or digested anaerobically or aerobically. Anaerobic digestion produces O biogas which can be used to generate electrical power and heat for the method of = the invention lowering the operating cost. The dry fraction obtained from anaer- N 35 — obic digestion can be spread like dry manure.

The method of the invention described above, including one or moresuccessive RO filtration steps, reduces the total amount of the nutrient rich frac- tion down to about 30 wt% from the original amount while up to about 70 wt% is processed into pure water. For example, when 10 000 kg of manure sludge is pro- cessed, 3 100 kg of dry manure (31 wt%) from the separation and centrifugation steps together, 700 kg of liquid fertilizer (7 wt%) obtained as a retentate from reverse osmosis and 6 200 kg of pure water (62 wt%) obtained as a permeate after two reverse osmosis steps are produced. This outcome is however indicative and can vary depending on the composition of the manure sludge and the pur- sued compositions of the various fractions obtained in the method. Furthermore, — the use of dewatering chemicals described above has an effect on the overall re- sult achieved by the method. Typical percentages by weight of the various fractions obtained from manure sludge by the method of the invention are described in Table 1 below. The proportions of the various fractions and dry matter contents thereof vary — with the composition of the manure sludge. “1st dry fraction” means a dry fraction derived from the separation step. “2nd dry fraction” means a dry fraction derived from the centrifugation step. “RO permeate” describes a permeate fraction de- rived from one or more successive reverse osmosis filtration steps. “RO retentate” describes the retentate derived from the first reverse osmosis filtration step. Combination of the first RO retentate with one or more further RO retentates ob- tained from the subsequent RO filtration steps does not significantly change the numerical values given for “RO retentate”. Table 1 It o sludge tion fraction tate ate & % | - %

RTF 5 mg O2/L 3 = 25 N Table 1 shows that phosphorus is extensively recovered in the dry fractions, especially in the second dry fraction. Nitrogen is fairly uniformly divid-

ed between the liquid and dry fractions. Nitrogen is then concentrated from the liquid fraction by reverse osmosis into an RO retentate. The method of the invention can be a continuous process or a batch process.

The fractions obtained in the method of the invention can be used as such as nutrient compositions. The fractions can also be arbitrary combined to provide formulations having desired nutrient compositions. For example, the dry fractions from the separation and centrifugation can be employed as a nutrient composition, as a soil conditioner, or as an energy source or for composting. The permeate fraction obtained from reverse osmosis filtration(s) is substantially free of dry matter and is mainly pure water with very low COD and nutrient content. The permeate fraction(s) can be led to the nature, or used as irrigation or flushing water, or as animal drinking water. The permeate can also be further purified in a water treatment plant, if appropriate. The concentrate(s) obtained from reverse osmosis filtration(s) can be used as a liquid fertilizer or further treated, for exam- ple, by evaporation or ammonia stripping. Another object of the invention is to provide an apparatus for treating manure sludge comprising: - a separator unit for separating manure sludge to a dry fraction and a first liquid fraction, - a centrifuge for removing solid matter from the first liquid fraction to provide a second liquid fraction, - one or more reverse osmosis units for concentrating the second liquid fraction. The apparatus of the invention is suitable for implementing the meth- od of the invention. o An embodiment of the apparatus of the invention is illustrated in Fig. N 3, including one reverse osmosis unit, and an optional second reverse osmosis A unit. The dashed lines indicate optional embodiments of the invention. In an em- 7 bodiment, the apparatus includes two reverse osmosis units. In an embodiment, the apparatus comprises a mixing unit upstream E from the separator unit to provide fairly homogenous manure sludge. N The apparatus can be arranged onto a transportable base, such as a O trailer, or can be constructed as a stationary plant. The capacity of the transport- = able unit can be for example 100 m3/h. An advantage of transportable unit is that N 35 the apparatus can be transferred between farms whereby need for stationary plants for manure sludge treatment in farms is reduced. The transportable unitcan be used without external electrical power and water source.

The transporta- ble unit thus provides a cost-effective and ecological alternative.

The capacity of the stationary plant can vary from a few to thousands of cubic meters per hour.

Manure sludge can be transported to the stationary plant by tankers or by pressure sewer.

The following example is presented for further illustration of the in- vention without limiting the invention thereto.

Example 1000 m3 of well mixed liquid cow manure sludge having a dry matter (DM) content of 8% was processed by a screw press (EYS SP600, mesh size: 0.5 mm) which resulted in two fractions: 250 metric tons of a dry fraction (“1st dry fraction”; DM 23%) and 750 m? of a liquid fraction (DM 3%). The liquid fraction was pumped to a decanter centrifuge (Andritz Sep- aration, model D5L, drum speed: 3200 rpm, differential speed: 3.9 rpm, torque: 55%, pond depth: 272 mm) which further removed suspended solids.

Processing by the decanter centrifuge resulted in two fractions: 760 m3 of a liquid fraction and 85 metric tons of a dry fraction (“20d dry fraction”). After centrifugation, the dry matter contents of the liquid fraction and the dry fraction were < 1% and 18%, respectively.

After centrifugation, the liquid fraction was pumped through a metal sieve with mesh size of 80 um to remove biggest particles.

After sieving, the resultant liquid was pumped to a reverse osmosis (RO) plant (DOW Filmtec SW30 membranes). In the RO, a volume concentration factor of 10 was used which produced 76 m? of retentate (“Liquid concentrate”) and 684 m3 of permeate.

DM contents of these fractions were 10% and < 0.1%, S respectively.

N To further purify the RO permeate, it was re-filtrated in the RO plant A (DOW Filmtec SW30 membranes) with a volume concentration factor of 50 which ? resulted again in two fractions: 14 m3 of retentate and 670 m3 of permeate (“Puri- = 30 fied water”). DM content of the retentate and that of the permeate were 5% and E <0.1%, respectively.

N Compositions of the fractions obtained above are shown in Table 2. O Percentage values are given on weight basis and calculated from total input 2 amount.

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Table 2 Manure 1st dry | 2nd dry | Liquid con- | Purified sludge fraction fraction | centrate water Proportion (96) | 100 | 22 | 9 | 7 | 62 | Dry matter (96) | 8 | 23 | 18 | 5 | <01 | (mg/kg) (mg/kg) (mg/kg)

4.6:1:4.4 | 3.7:1:1.6 | 3.1:151 | 1:0:13 | 13:0:1 Chemical oxygen >20 000 15 demand mg O2/L It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The inven- tion and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

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Claims

1. A method for treating manure sludge comprising the steps of: - providing manure sludge, - subjecting the manure sludge to separation to provide a first dry frac- tion and a first liquid fraction, - subjecting the first liquid fraction to centrifugation to provide a sec- ond dry fraction and a second liquid fraction, - subjecting the second liquid fraction to one or more sequential re- verse osmosis (RO) filtration steps to provide one or more RO retentates and one or more RO permeates, wherein the feed for each subsequent RO filtration step is an RO permeate obtained from the previous RO filtration step and wherein the dry matter content of the permeate obtained after one or more RO filtration steps is <0.5%.

2. The method of claim 1, comprising a step of mixing of the manure sludge prior to the separation step.

3. The method of claim 1 or 2, wherein the separation is carried out with a screw press.

4. The method of any one of the preceding claims, wherein the centrif- ugation is carried out with a decanter centrifuge.

5. The method of claim 4, wherein the drum speed of the decanter cen- trifuge is in the range of 2000 to 5000 rpm.

6. The method of claim 4 or 5, wherein the differential speed of the de- canter centrifuge is in the range of 0 to 20 rpm.

7. The method of any one of the preceding claims, wherein the dry matter content of the first dry fraction is in the range of about 15% to about 35%. N

8. The method of any one of the preceding claims, wherein the dry N matter content of the second dry fraction is in the range of about 15% to about 3 2596. =

9. The method of any one of the preceding claims, wherein two se- E 30 quential RO filtration steps are involved, wherein the second liquid fraction is N subjected to a first RO filtration step to provide a first RO retentate and a first RO O permeate, and the first RO permeate is subjected to a second RO filtration steps to © provide a second RO retentate and a second RO permeate. N

10. The method of any one of the preceding claims, wherein the dry matter content of the retentate obtained from the first RO filtration step is in the range of about 1% to about 15%.

11. The method of any one of the preceding claims, wherein COD of the permeate obtained after one or more RO filtration steps is <15 mg 0O2/L.

12. The method of any one of preceding claims, wherein the N:P:K ra- tio of the permeate obtained after one or more RO filtration steps is 1-2:0:1.

13. Apparatus comprising units for implementing the method of any one of claims 1-12, comprising: - a separator unit for separating manure sludge to a dry fraction and a first liguid fraction, - a centrifuge configured to receive the first liguid fraction from the separator unit and to remove solid matter from the first liquid fraction to provide a second liquid fraction, - one or more reverse osmosis (RO) units, one of which is configured to receive the second liquid fraction from the centrifuge and to concentrate the second liquid fraction, wherein the feed for each subsequent RO unit is an RO permeate obtained from the previous RO unit.

14. The apparatus of claim 13, further comprising a mixing unit up- stream from the separator unit to provide fairly homogenous manure sludge.

15. The apparatus of claim 13 or 14, wherein two reverse osmosis units are present.

16. The apparatus of any one of claims 13-15, which is arranged onto a transportable base, such as onto a trailer. o

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